1. Field of the Invention
The present invention relates to receiving technologies and it particularly relates to a receiving method for receiving signals by a plurality for antennas and a receiving apparatus.
2. Description of the Related Art
In wireless communication, it is generally desired that the limited frequency resources be used effectively. Adaptive array antenna technology is one of the technologies that can realize effective utilization of frequency resources. In adaptive array antenna technology, the amplitude and phase of signals transmitted and received by a plurality of antennas, respectively, are so controlled as to form a directional pattern of the antenna. In other words, the apparatuses provided with adaptive array antennas change the amplitude and phase of signals received by a plurality of antennas, respectively, add up the thus changed received signals, and receive the signals equivalent to the signals received by the antenna having the directional pattern corresponding to the variation in the said amplitude and phase (hereinafter referred to as “weight”). In addition, signals are transmitted in a directional pattern of the antenna corresponding to the weight.
One example of processings for weight computation in adaptive array antenna technology is a processing based on the MMSE (Minimum Mean Square Error) method. In the MMSE method, the Wiener solution is known to be the condition for an optimum weight value. Also known is a recurrence formula with smaller amounts of calculation than directly solving for the Wiener solution. For such recurrence formulas, adaptive algorithms, such as RLS (Recursive Least Squares) algorithm and LMS (Least Mean Squares) algorithm, are used.
Also where adaptive array antennas are not used, there exist phase errors, which are normally called frequency offset, in the signals generated by a local oscillator in a transmitting apparatus as well as in the signals generated by a local oscillator in a receiving apparatus. For example, when a phase modulation, such as QPSK (Quadrature Phase Shift Keying), is used for modulation between a transmitting apparatus and a receiving apparatus, the QPSK signal points on the constellation of the signals received by the receiving apparatus rotate due to phase errors. Since the rotation of signal points like this lowers signal transmission quality, an automatic frequency controller (AFC) is normally provided in a receiving apparatus to prevent it (see, for example, Reference (1) in the following Related Art List).